verify: report first bad changeset - add linkrev and file arguments to err - track lowest reported linkrev in err - find linkrev in a couple cases - sort linkrevs when reporting a bunch of errors against a file - tidy up lots of messages - make more robust against damaged indexes - report first bad changeset if an error is encountered

a -> a not a symlink
a -> b
Now at: base.patch
applying symlink.patch
Now at: symlink.patch
a -> b